Method and composition for treating metal surfaces

ABSTRACT

The disclosed composition and method are useful for imparting corrosion resistance to metal surfaces. Predominately iron, aluminum or zinc surfaces are treated with an aqueous solution comprising phosphate ions, simple fluoride ions, chlorate ions and one or more Group VIIIb metal cations in specified concentrations. The composition contains essentially no bromate or &#39;&#39;&#39;&#39;coating-metal&#39;&#39;&#39;&#39; cation. Metals treated with the disclosed composition are particularly suited for treating metals which are to be subsequently painted and subjected to cold forming.

United States Patent 1191 Russell et al.

METHOD AND COMPOSITION FOR TREATING METAL SURFACES Inventors: William S. Russell, Warren; Gary A.

Reghi, Detroit, both of Mich.

Assignee: Oxy Metal Finishing Corporation,

Warren, Mich.

Filed: Dec. 1 1, 1972 Appl. No.: 314,077

Related U.S. Application Data Continuation-in-part of Ser, No. 154,156, June 17, 1971, abandoned.

U.S. Cl. I48/6.l5 R, 148/627 Int. Cl. C23f 7/10, C23f 7/14 Field of Search 148/615 R, 6.15 Z, 6.27,

References Cited UNlTED STATES PATENTS [4 ]v June 25, 1974 Primary Examiner-Ralph S. Kendall Attorney, Agent, or Firm-Marvin Trimas; Arthur E. Kluegel; B. F. Claeboe 5 7] ABSTRACT The disclosed composition and method are useful for imparting corrosion resistance to metal surfaces. Predominately iron, aluminum or zinc surfaces are treated with an aqueous solution comprising phosphate ions, simple fluoride ions, chlorate ions and one or more Group Vlllb metal cations in specified concentrations. The composition contains essentially no bromate or coating-metal cation. Metals treated with the disclosed composition are particularly suited for treating metals which are to be subsequently painted and subjected to cold forming.

10 Claims, No Drawings METHOD AND COMPOSITION FOR TREATING METAL SURFACES CROSS-REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of Ser. No. 154,156 filed June I7, 1971 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to the art of treating metal surfaces for the purpose of converting the surface to a corrosion resistant and paint receptive phosphate layer.

Numerous compositions have been developed for the treatment of metal surfaces to impart corrosion resistance by converting the surface to a phosphate layer. To be effective, this layer must be adherent to the metal surface in order to protect the metal surface from corrosive influences. Adhesion is of special importance if the metal is to be cold formed following treatment because the phosphate layer is subject to great stress.

The simplicity and economics of phosphatizing processes could also be greatly improved if it were possible to treat a variety of metal surfaces with a single bath. Existing processes normally require a complete change of baths when it is desired to change the metal treated. In other cases, component proportions in the bath or a change in the treating time is required. For example, when processing aluminum, it has been found that too light a coating will be obtained if too little fluoride is present. Conversely, if too much fluoride is present, an undesirably heavy coating may be obtained. It is an object of this invention to provide a composition which can be used to provide a corrosion resistant coating which possesses good adherence characteristics in spite of subsequent cold forming operations and which may be used to treat aluminum, zinc, and iron or alloys containing a predominate proportion of one of these metals.

SUMMARY OF THE INVENTION The present invention is directed to an aqueous noncoating bromate-free solution useful for treating iron, zinc and aluminum surfaces or their alloys which bath comprises phosphate in the range of about 0.025 to percent by weight; chlorate in the range of about 0.07 to percent by weight; simple fluoride in the range of about 0.001 to 2 percent by weight; metallic cations selected from Group Vlll(b), metals of the periodic table of the elements having atomic numbers from 26 to 28 in the range of about 0.001 to 0.5 percent by weight; and one or more additional cations selected from the group consisting of hydrogen, ammonium, and the alkali metals. This solution is particularly useful for treating two or more of the foregoing metal surfaces sequentially, when interspersed on a treating line, or when components of a single multi-metal article.

British Pat. No. 912,400 discloses a solution for treating aluminum surfaces. The solution must contain alkali metal phosphates, bromate ions, simple fluoride ions, and may contain chlorates. The solution of the present invention additionally contains a group Vlll(b) metal ion, must contain a chlorate ion, and must not contain the bromate ion. Comparative tests of the bromate containing composition versus the composition of the present invention showed the present invention to be highly advantageous. Comparative examples are contained in the detailed description of the invention.

The individual components of the present invention have been taught useful for metal treating on numerous patents and publications. However neither the claimed combination nor the advantages of its use have been recognized in the art.

DETAILED DESCRIPTION OF THE INVENTION All percentages are by weight unless otherwise specified.

The present invention is concerned with a metal treating bath and the method of treating metals therewith. The bath of the present invention is an aqueous non-coating bromate-free solution useful for treating iron, zinc or aluminum surfaces, or alloys containing a predominate portion of one of said metals, to form a phosphate coating thereon which coating will satisfactorily'withstand subsequent cold forming deformations comprising: phosphate ions in the range of about 0.025 to 10 percent; chlorate ions in the range of about 0.07 to 15 percent; simple fluoride ions in the range of about 0.001 to 2percent; one or more first cations selected from the group Vlll(b) metals of the Periodic Table of the elements, having atomic numbers of from 26 to 28, in the range of about 0.001 to 0.5 percent preferably 0.001 to 0.05 percent; and one or more second cations selected from the group consisting of hydrogen, ammonium, and the alkali metals, said solution being substantially free of any coating non-alkali metal. The pH of the solution is preferably between 3.2 and 6.0. The free acid concentration of the solution is advantageously less than about I and preferably approximately 0. Preferably, the phosphate ion concentration is in the range of about 0.2 to 2.5 percent; the chlorate concentration is in the range of about 0.5 to 7.0 percent; and the fluoride ion concentration is in the range of 0.01 to 0.3 percent. In a particularly preferred embodiment, the group Vlll(b) metal is cobalt.

The metal surface is treated with the above composition after it has been cleaned. For example, the metal may be cleaned with a variety of cleaners such as alkali or acid-based cleaners, then water rinsed and followed by a treatment with the above composition. Following this treatment, the metal surface is again water rinsed and if desired given a passivating rinse prior to application of the final protective paint coating.

This invention is applicable to treatment of zinc, iron, or aluminum surfaces or alloys of any of these metals in which one of these metals predominates. The most common zinc surfaces are those obtained by the galvanizing of steel whereas the iron containing surfaces are most often cold-rolled steel.

The precise manner in which the components are combined to form the aqueous solution is not material. It should be kept in mind that the present invention pertains to a noncoating bath. This means that neither zinc, manganese, nor any other metal ion entering the conversion layer in appreciable quantities are added to the bath. The cation portion of the coating formed on the surface of the metal in question is composed almost completely of the metallic cations derived from the metal surface itself. Therefore, the phosphate ions can be'added to the aqueous solution either in the form of phosphoric acid and/or alkali metal phosphates but cannot be added in the form of zinc dihydrogen phosphate or the like.

It is also critical to the operability of the present invention that the floride ions be present as a simple fluoride ion in the solution. In other words, the fluoride ions cannot be present in the form of a complex such as a fluoborate or fluosilicate. Therefore, the fluoride ion must be added as the simply hydrogen fluoride or alkali metal or ammonium fluorides or bifluorides. The presence of complex fluorides in the solution will result in inferior products and will also contribute substantially to sludge formation and related degredation of the treating bath. It is surprising that simple fluoride ions are beneficial when added to a non-coating bath and all known prior art publications dealing with noncoating type baths require that fluoride present be in the form of a complex fluoride. The exception is the previously discussed British patent 912,400 which is distinguished for other reasons. In keeping with the foregoing requirements, the chlorate ion may be introduced as the alkali metal or ammonium chlorate. Another necessary component in the solution in a cation of a group Vlll(b) metal having atomic number 26 through 28, namely, nickel, cobalt or iron. These cations may be introduced as any of the common water soluble salts such as acetate, chloride, nitrate, sulfate,

etc.

The pH of the treating solution is preferably between 3.2 and 6.0 and preferably less than 5. The free acid of the solution, defined as the milliliters of H10 normal sodium hydroxide which must be added to a 10 ml. sample to reach the bromo cresol green end point, should be about 0. In some cases, the free acid number may become negative. This means that the solution must be back titrated with 0.1 N sulfuric acid in order to approach the bromo cresol green end point from the other direction.

Suitable treatment temperatures are between about 100 F and the solution boiling point and preferably 155 to 170 F and most preferably at about 160 F. The treating may vary from about 5 seconds to about 5 minutes depending upon the temperature and particular composition employed. Both spray and immersion techniques are suitable.

EXAMPLE 1 After cleaning and hot water rinsing hot-dip galvanized steel, the metal surface was sprayed at 155-l70 F with an aqueous composition containing the following ions:

4 percent by weight C101,

I 1 percent by weight P 0.1 percent by weight F 0017 percent by weight Ni The metal surface was then rinsed with cold water and rinsed with a hexavalent chromium solution. Separate metal surfaces were then painted with a series of paints, such as Dulux (trademark of DuPont for alkyd paint), Butler vinyl and an acrylic paint.

Each of the surfaces achieved satisfactory results in adhesion, forming (bending) and impact deformed testing. Satisfactory results were also obtained in the salt spray test and accelerated humidity test 100 percent humidity for l-4 weeks).

Cold rolled steel and aluminum surfaces were treated in an equivalent manner with similarly satisfactory results.

EXAMPLES l 9 The following examples demonstrate the advantages to be obtained using the solution of the present invention. For all of the cold-rolled steel panels the following procedure was followed:

1. Alkaline cleaning at 160 F for 30 seconds.

2. Hot Water Rinse.

3. Spray treatment with phosphatizing solution at 160 F for 10 seconds.

4. Cold Water Rinse.

5. Final rinse at F with-hexavalent chromium passivating solution for 3 seconds.

6. Painting with a gold metallic vinyl-based paint obtained from Continuous Colour Coat, Canada.

The hot dip galvanized panels were processed as follows:

1. Alkaline rinse at l60 F for 15 seconds.

2. Second rinse with titanate containing cleaner Ti(- SO0 at F for 5 seconds.

3. Spray treatment with phosphatizing solution at F for 10 seconds.

4. Cold water rinse.

5. Final rinse at 130 F with hexavalent chromium passivating solution for 3 seconds.

6. Painting with Super-Clad 510 paint (a vinyl-based paint manufactured by Sherwin-Williams Paint Co.) and a white solution vinyl paint obtained from Continuous Colour Coat.

The aluminum (3003 alloy) panels were processed as follows:

1. Alkaline cleaning at 160 F for 15 seconds.

2. Hot Water Rinse.

3. Spray treatment with phosphatizing solution for 10 seconds.

4. Cold Water Rinse.

5. Final rinse at 130 F with hexavalent chromium for 3 seconds.

6. Painting with Super-Clad 510 vinyl-based paint.

In all instances, the surfaces were treated with the solution of the present invention by the spray technique for a period of ten seconds. In each case, the phosphate content of the bath was approximately 1 percent and the chlorate content was approximately 4.2 percent. The concentration of the fluoride ions and cobalt or nickel ion are as indicated in the tables.

In the table, the coating weight and metal loss are in mg/ft of metal surface. Metal loss'data are obtained by comparing the original weight of a panel prior to phosphatizing to the weight of the panel after the phosphate coating has been stripped away. The adhesion data are obtained by the O-T bend test in which the painted metal panel is bent and pressed so that the back surfaces are in contact after which transparent tape is applied to the bend and removed to collect any nonadherent paint. This is the most severe test of the adhesive strength of a coating subjected to deformation. In the 2-T bend test, the panel is folded in so that the bend tested is wrapped around two thicknesses of the panel. This test is less severe than the OT test.

The adhesion data are evaluated based upon the following system:

-Continued Rating 71 Paint Loss to Tape Ill -257z 11 Z5507Z 1 50-10071 Since the OT test is the most severe, samples exhibiting relatively high paint loss may still be acceptable to some manufacturers depending on their type of operations. 7 7 V v For cold-rolled steel, the use of cobalt is clearly superior to nickel. Metal losses are a measure of process efe ya e apptex tsly 3MQP9PIJ f r.

TABLE 1 USE OF COBALT VS. NICKEL FOR CRS The panels were processed as in Tables 1 and 11 except that the phosphatizing was by immersion rather than spray application.

Free Coating Metal Adhesion Example %Ni %Co* %F' Acid pH Weight Loss OT (b) 0 0.016 0.022 0 3.70 45.0 39.6 V 3 (a) 0.016 0 0.022 0.2 4.10 38.1 42.6 1.

(b) 0 0.016 0.022 0.1 4.19 48.7 28.8 V 4 (a) 0.016 0 0.10 0 3.9 28.8 66.9 1 (b) 0 0.016 0.10 0 3.8 38.7 43.2 V 5 (a) 0.016 0 0.10 0.6 4.2 23.8 37.2 1

(b) 0 0.016 0.10 0.2 4.0 30.6 35.4 V (c) 0 0.016 0.10 0.6 4.4 27 22.2 V

TABLE I! USE OF COBALT US NICKEL ON ALUM AND HDG Metal Free Coating Adhesion Example Treated %Ni %Co" %F' Acid pH Weight O-T 2-T 6 (a) Alum 0.016 0.10 0 3.8 45.6 1 1 (b) 0.016 0.10 0 3.8 12.6 1 111 7 (a) Alum 0.016 0.10 -0.6 4.2 51.3 11 (b) 0.016 0.10 0.6 4.2 45.0 V 8 (a) Alum 0.016 0.022 0 3.7 11.0 V (b) 0.016 0.022 0 3.7 11.0 V 9 (a) HDG 0.016 0.10 0 3.8 77.1 V (b) 0.016 0.10 0 3.8 51.1 V

the cobalt system. While the cobalt system consistantly Table III demonstrates that the addition of a small gives adhesions of V, the nickel adhesion is consistantly quantity f bromate results i a d m decrease i d.

For aluminum treating, the cobalt system is as good or better than the nickel depending on the concentrations employed. Both systems appear equally suitable for treating hot dip galvanized surfaces.

When one attempts to treat a hot dip galvanized surface with the composition of the present invention but containing no Group Vlll(b) metal, completely unacceptable adherence characteristics are obtained with paint loss under O-T conditions approximating 100 percent.

EXAMPLES 10-12 Table 111 compares adhesion property variations as a function of bromate content. In each example the basic bath was approximately as follows:

POI" 1% C10; 4.2% Ni 0.016% P 0.1% Free Acid 0.3 pH 3.55 Treating Time 10 seconds hesion in the case of hot dip galvanized. It is essential that the bath be substantially bromate-free if it is to be suitable for treating hot dip galvanized surfaces.

What is claimed is:

I 1. An aqueous non-coating bromate-free solution useful for treating any of iron, zinc or aluminum surfaces or alloys containing a predominate portion of one of said metals to form a phosphate coating thereon which coating can satisfactorily withstand subsequent cold forming deformations, comprising: phosphate ions in the range of about 0.025 to 10 percent by weight;

chlorate ions in the range of about 0.07 to 15 percent by weight; simple fluoride ions in the range of about 0.001 to 2percent by weight; one or more first cations selected from the group Vlll(b) metals having atomic numbers of from 26 to 28 in amounts between about 0.001 and 0.5 percent by weight; and one or more sec- 2. The solution of claim 1 wherein the pH is between about 3.2 and 6.0.

3. The solution of claim 1 wherein the free acid is about 0.

4. The solution of claim 1 wherein said Group VlII(- b) metal is cobalt.

5. The solution of claim 1 comprising phosphate ions in the range of about 0.2 to 2.5 percent by weight; chlorate ions in the range of about 0.5 to 7.0 percent by weight; and fluoride ions in the range of about 0.01 to 0.3 percent by weight.

6. The method of treating metals prior to cold forming comprising contacting the surface of said metal with a solution comprising phosphate ions in the range of about 0.025 to 10 percent by weight; chlorate ions in the range of about 0.07 to percent by weight; simple fluoride ions in the range of about 0.001 to 2 percent by weight, one or more first cations selected from the group VlII(b) metals having atomic numbers of from 26 to 28 in amounts between about 0.001 and 0.5 percent by weight; and one or more second cations selected from the group consisting of hydrogen, ammonium and the alkali metals, said solution being substantially free of coating non-alkali metals.

7. The method of claim 6 wherein'the solution pH is between about 3.2 and 6.0.

8. The method of claim 6 wherein the free acid is about 0.

9. The method of claim 6 wherein the Group VlII(b) metal is cobalt.

10. The method of claim 6 wherein said solution comprises phosphate ions in the range of about 0.2 to 2.5 percent by weight; chlorate ions in the range of about 0.5 to 7.0 percent by weight; and fluoride ions in the range of about 0.01 to 0.3 percent by weight. 

2. The solution of claim 1 wherein the pH is between about 3.2 and 6.0.
 3. The solution of claim 1 wherein the free acid is about
 0. 4. The solution of claim 1 wherein said Group VIII(b) metal is cobalt.
 5. The solution of claim 1 comprising phosphate ions in the range of about 0.2 to 2.5 percent by weight; chlorate ions in the range of about 0.5 to 7.0 percent by weight; and fluoride ions in the range of about 0.01 to 0.3 percent by weight.
 6. The method of treating metals prior to cold forming comprising contacting the surface of said metal with a solution comprising phosphate ions in the range of about 0.025 to 10 percent by weight; chlorate ions in the range of about 0.07 to 15 percent by weight; simple fluoride ions in the range of about 0.001 to 2 percent by weight, one or more first cations selected from the group VIII(b) metals having atomic numbers of from 26 to 28 in amounts between about 0.001 and 0.5 percent by weight; and one or more second cations selected from the group consisting of hydrogen, ammonium and the alkali metals, said solution being substantially free of coating non-alkali metals.
 7. The method of claim 6 wherein the solution pH is between about 3.2 and 6.0.
 8. The method of claim 6 wherein the free acid is about
 0. 9. The method of claim 6 wherein the Group VIII(b) metal is cobalt.
 10. The method of claim 6 wherein said solution comprises phosphate ions in the range of about 0.2 to 2.5 percent by weight; chlorate ions in the range of about 0.5 to 7.0 percent by weight; and fluoride ions in the range of about 0.01 to 0.3 percent by weight. 